The Six
by sassypress
Summary: Once again the world is plummeting into chaos and Percy Jackson must rise to the occasion. A prophecy has claimed that the six children of the Big Three are to set out and save the world, but the numbers don't quite add up. X-over between Percy Jackson & the Olympians and The Heroes of Olympus.
1. The Prophecy

Demigod Chp 1

The sun was shining with burning heat, yet Camp Demigod paid no mind, already well into the hustle and bustle of the day. Summer had just begun and campers were beginning to overcrowd the camp like ants. Percy Jackson looked out over the lake, feeling the humid air wash over him like a familiar hug. He inhaled deeply, appreciating the New York greenery. Percy and his girlfriend Annabeth had just finished their second year of college at UC Berkeley, just minutes away from the city of New Rome. It had been 3 years since the Greek and Roman demigods had been introduced to each other's worlds, Percy was the son of Poseidon and had been working closely with Jason Grace, son of Jupiter, to bring peace and harmony to the two camps. After high school Percy and Jason traded places; Percy went to become a leader of New Rome in California while Jason spent the years in New York helping to run Camp Demigod at the side of his girlfriend Piper.

Yet nothing could beat summers in New York, Percy returned every year and there truly is no place like home.

"Ahem, Percy?" Percy turned and smiled. Annabeth wore her training armor and a frown, "There's a visitor and something you ought to hear."

"Oh gods, not another food fight, we don't need a random inspection in the middle of the summer start up chaos," Percy half walked, half ran to the camp entrance beating muttering to himself about messy children and their all too realistic food wars. He punched in the code to the conference room and came face to face with two more demigods, an oracle, a centaur, and a goddess.

"Uh oh, this doesn't seem like a routine inspection," Percy sat down in one of the chairs next to Jason Grace and Leo Valdez, Annabeth nodded curtly at the centaur and left the room.

Chiron had been growing out a rather elaborate beard for the last few months and his trail was neatly groomed, "We have a prophecy directly from a goddess." He gave a quick nod in the direction of the goddess, "Rachel, why don't you read the prophecy,"

The girl with flaming red hair stood up and closed her eyes in concentration. As she spoke her voice became soft and powerful, "

 _Six children of the three_

 _A girl and a boy of each_

 _Shall traverse through the sea_

 _The end of the worlds they shall seek_

 _A matter of time: a fortnight_

 _Til darkness breaks free_

 _Held only by the chains of time_

 _To meet inevitability at the gate of escape_

 _And battle the patron for power_

 _Should she lose the fire will burn out_

Rachel sat down looking faint and Chiron went to fetch her a glass of water. Percy, Jason, and Leo turned to the goddess in the corner.

The goddess had dozens of brown curls framing her heart shaped face and her eyes were warm like the campfires outside, "I am Vesta, or Hestia to the Greeks. An old prophecy has resurfaced and I am at war."

"Aren't you supposed to be a peaceful goddess? Like you've never been involved in war before have you?"

"No I have not, but I am the patron the prophecy speaks of. There has been an underground war brewing for years; the primordial deity Ereubus has grown restless of his powerless state, he is darkness in its very first form. For centuries Chronos, not to be confused with the Titan Cronos, has tried to keep Ereubus under control. But Chronos is weakened, the time god has run out of time. In two weeks Ereubus will reunite with his wife, Anake the goddess of inevitability. If they meet and battle me side by side, I will lose my city, and the world will fall into darkness."

"Well not to poop on the party even more, but what can we do about it?" Leo brushed his dark curls out of his eyes. He was shorter than Jason and Percy, skinnier too, but that was fine, it had come in handy many times before.

"You are the fire walker boy no?" Leo nodded, "You will not be going on this journey, but I have been told you are a master carpenter."

"I see, you want me to make something for you," Leo leaned his chair back and crossed his arms.

"Actually, you've already made it. The ship." Leo gave a small gasp. 'The ship' was a magnificent structure based off his robotic shapeshifting dragon. It was a luxury cruise aboard a battleship and Leo had spent the last year working on it tirelessly.

"But, but it's not ready!" Leo ran out of the room, probably to go work on his masterpiece. He knew that the goddess was right, if Jason and Percy needed the _Armada_ then they would just have to have it.

With Leo gone Jason and Percy turned towards the goddess, "so when do we leave? Or at least meet up with the others, we're kinda missing more than half our team here"

"Your sisters and Hazel Levisque and Nico DiAngelo will meet you here tonight. Also it is in your best interest to have a proper goodbye to any of your friends staying behind, hopefully you will see them again. I expect great things from you. "

With that the goddess stepped into the fireplace and disappeared, leaving behind only a small pile of ash.

Percy and Jason sat in silence for a second before Percy jumped out of his chair, he turned to Chiron with wild eyes, "Wait! She said sisters! As in both of us, as in I have a sibling," Percy sat down and put his head in his hands, he'd always been an only child, and now two decades after his birth a goddess was alluding that he had a long lost sister.

Chiron chuckled, "Yes, well I suppose it is time that you become acquainted with the daughter of Neptune."


	2. Cassie

Cassie Virtanen was not having a good day. It was the first official day of summer and Cassie was spending the day packing to go on a vacation she didn't ask to go on. Well it wasn't really a vacation either, at 11 AM Mercury, God of Annoying Messengers, showed up at her doorstep and told her to pack her things to go to New York. He went on to tell her parents how she had gotten a job as a camp counselor for children interested in STEM fields and there had been a major technical difficulty and that if Cassie could leave tonight the camp would pay for her plane ticket, and that a flight was already booked. And naturally her parents were overjoyed, "a great resume booster" they said. Never mind that Cassie had only been back in El Paso for 2 weeks after returning from her first year of college.

So Cassie sat on the floor of her room, her black hair pulled into a messy half-bun, the other half falling down to her mid-back in natural beach waves. She pulled together her hiking and swim gear, regular clothes, and few snacks into a large backpack. She went downstairs and saw Mercury draped over her favorite couch chair. He smirked when he saw her frown.

"Now pussycat don't be sad, soon you'll see you're big brother."

"Wait. What? Where exactly are we going?"

Mercury bit his lip, "I probably shouldn't have said that, but yeah you've been called to a prophecy. And so has Percy. Actually, so have all the children of the Big Three."

"That might have been good information to disclose," Cassie went down the hall to hug both her parents goodbye before heading out the door with Mercury. He led her down the street to his motorcycle. She looked up at Mercury is disbelief, "You've got to be kidding me,"

"Sorry pussycat, it was the only thing available back at shop" Mercury shrugged and hopped on the bike, and Cassie managed to squeeze into the sidecar, hugging her knees to her chest. They took off and soon were flying through the sky at lightning speed.


	3. The Daughter of Neptune

Chapter 3

Mercury's motorcycle touched down onto a grassy field. Cassie tumbled out of the sidecar and stumbled towards the edge of the field, heaving. Flying was not her natural element and always made her stomach unsettled. She collected herself and took in her surroundings.

"Where are we? It's so… Green" they stood in the midst of a forest, large trees arching over their heads.

Mercury shrugged, "We're about a quarter mile from Camp Demigod? Haven't you been here before?"

"Naw, whenever I'm on the East Coast I'm directly in Olympus. Or Florida, Dad has me do some work with wildlife there sometimes.

"Well, this is where the normal demigods go. The Greek ones at least. C'mon, we better start walking before it gets dark."

"Merc it is dark, why did we have to park half a mile away from the Camp?"

"Quarter of a mile," Mercury started the trek through the trees, "grab your bags and start walking, exercise is good for you doll."

They hiked up the hill and reached a rusty gate, Cassie adjusted her bag and grunted. "This is it? I mean I wasn't expecting much but this is dull."

"Darling, don't just look, you have to see through the glamours."

Cassie took a step forward and squinted, really concentrating on breaking through the magical barriers. Once she did she was awestruck.

Behind the gate dozens of kids, big and small, ran around the camp. They spared, feet moving at the speed of light. They laughed and chatted, the sounds echoing off the cabins adorned in decorations. A campfire was lit as the sun set over the edge of a glistening lake.

Cassie smiled. She had never spent a lot of time with other demigods, even Roman ones, as a result of her special condition. Camp Demigod felt warm, it was inviting and exciting, it felt like the home she'd been searching for so long. Mercury pushed the gate open effortlessly and it squealed so loudly that half the camp stopped what they were doing to look at the source of the noise.

Then the other half of the camp stopped to stare at the visitors. It wasn't often a god personally escorted a demigod, and rarely a demigod whose hair had expanded twice the size of its natural state from humidity and a dirt smeared face (Cassie was not prepared for the impromptu hike).

One brave kid stepped forward and stared at Cassie with curiously, "So who are you?"

"Oh right, I'm Cassie, I'm kind of lost, can someone show me to the welcome center so I can wash my face."

The kid, who was named Bran, took Cassie's hand and led her to the big building in the middle of camp. Sensing his que to leave, Mercury winked at Cassie and left camp, the gates swinging shut behind him.

Cassie freshened up and went to sit in the common area, she skimmed through tabloid magazines until the front doors opened.

Three boys and two girls walked in. The first boy was tall and lean, he had bronzed skin and his hair clean cut and combed. He held hands with one of the girls, she was one of those girls who was gorgeous beyond belief but didn't give a care in the world, her chocolate brown hair was tied in a messy braid and she wore an orange t-shirt and jean shorts. The boy behind them was the shortest in the group, he had dark brown curls that covered his eyes and his burly arms were covered in streaks of ash. The blonde girl who stood next to him had bright grey eyes, the kind that appear to analyze every little thing every single second.

And then Cassie saw him, and even though they looked like opposites, she knew who he was immediately. The only thing recognizable between the two of them was their jet black hair. His contrasted with his pale skin, and on anyone else he would have looked ill. Except Percy Jackson was not just some other boy, he was the brother Cassie had never known, the forbidden family she wasn't allowed to see.

"Hi, I'm Cassandra, Cassie for short," Cassie stood up and reached her hand out to the tall boy up front.

"Jason" when he shook her hand a spark jolted her body, "sorry about that, I get kind of electric sometimes."

Introductions went around the room until they came to Percy. He didn't say anything but stepped forward and hugged Cassie, "Cassie, it's so good to meet you. I didn't even know you existed until this morning, and I doubt you knew about me-"

"I did." Cassie knew she wasn't supposed to talk about it, but it was a secret she'd been holding in for almost a decade."

"Wait, you did?"

Cassie gestured to the couches and the group sat in front of her as she explained the story of her life "I found out about my… Heritage- when I was in 4th grade. You, Percy, had just saved the world for the first time and the gods were worried. Your destiny had been written for years before you were born, and I was never intertwined with it. So I guess I have to start from the beginning."

"You were born the son of Poseidon. I was born the daughter of Neptune. However, the similarities in our father pretty much end at him being the God of the Sea. Poseidon was revered by the Greeks; Neptune was feared by the Romans. Poseidon was hospitable, pleasant, and generous. Neptune had a temper, little patience, and a bad reputation. So naturally, a daughter of Neptune was not so well received. When I was born it was a mistake, my mother was not, um, adjusted to a god being the father of her kid and the trouble that would come with having a demigod daughter. So my dad came up with a solution. He switched me at birth to an Army couple stationed in the area. My adopted parents don't know they adopted me, I didn't either until Diana showed up at my house when I was 9."

"Diana? Like the goddess Diana?" Jason stared at Cassie in shock. It wasn't often gods appeared to their children, even less often that other gods did the work for them.

"Yes, the goddess Diana. By now my family had settled down in El Paso, a landlocked city. Diana was in the area and I was starting to display subtle demigod powers but they were subdued since I was far from my element. Being so far inland and in the desert made it safer for me to be alone and without support from places like Camp Demigod or New Rome."

"Anyways, Diana explained who I really was and it took me a while to believe her, like I had to fight a half-giant first. But I guess I've always liked learning the hard way. So I've spent the last nine years looking in on a world that I couldn't be a part of. If Percy knew about me I would be a liability, think of me as the best kept secret on the planet. Only the gods know my heritage and now you five. I was isolated from other demigods and acted like a regular mundane, but served the gods on my free time. Like you know how Nico DiAngelo acts as a pseudo ambassador to the underworld?" The others nodded, "well that's kind of my job. My official job title is Executive Liaison to the Governing Authority of the Sea, aka I clean up Daddy's messes when he fights with his brothers. It's cool, I get free room and board to Olympus and New Rome and my dating standards are kind of high now since most of my exes are gods. But yeah, that about wraps up most of it."

The others were quiet for a second, finally Percy broke the silence, "Shit. That's really cool and all, but I wish Dad told me about you. It would have been cool to have a sister growing up, how old are you?"

"I'm eighteen, only two years younger than you."

Annabeth leaned forward, a scowl on her face, "Why should we believe anything you just said? None of us have ever heard of you. And you're Roman, you say you've been to New Rome, but there's never been a mystery demigod at camp, how do we know you are who you say you are?"

Cassie prickled, "You think I'm lying daughter of Athena? I've been watching all of you for years from the sideline, next to the gods. I may not be a 'classically' trained demigod but I sure as hell have skills."

"You said no one likes your dad, he's abrasive and hard to work with, so why should you, a stranger go on this quest?"

"I've been called to duty, and I won't ignore a prophecy like this. My father may have his flaws, but I am not my father. That's like saying only children of Athena can be smart, when in reality maybe the rest of us are clever too. Don't make assumptions about someone based on their parents."

Annabeth stood up, and eyed Cassie, "I don't trust you."

Cassie stood up, level to Annabeth, the air became dry with tension and Percy stood up to try and calm the two girls, "You don't want to start with me."

The air got drier and it became obvious that the New York humidity was attracted to Cassie as she began to glisten, "Children of Athena have always been so arrogant and self-righteous. Listen here, you may be smart, but you're not hot shit."

Percy stood in between his girlfriend and sister, "Annabeth, Cassie just got here, cut her some slack. She's obviously not new to the whole godly quest situation, I trust her. She's my sister and she's been called to this prophecy."

Annabeth sat down and Cassie followed, her brown eyes cold as ice. Percy turned to his sister, "How did the adoption work out? Do you know your birth mother?"

"Oh yeah, she's a stripper on Miami Beach."

Jason snickered behind his hand and Piper jammed her elbow into his stomach. "Oh, you're not joking?"

"Nope, even the gods have one night stands. And Poseidon/Neptune happens to have a thing for black-haired beauties," she gestured at her and Percy's jet black hair, "That's why my existence became such an issue. Percy was written into the fates when Poseidon met Sally, but no one could predict for a Cuban-American stripper from Miami Beach getting knocked up with a demigod. I was an accident, and Neptune did his best to make sure I wouldn't interfere with Percy's fate."

"Oh shit, that's some heavy stuff. I'm sorry," Piper rolled her eyes as Jason rubbed his side.

Cassie shrugged, "It's no biggie, I don't know many demigods, but I know a ton of gods. Your mom is actually one of my best friends." Cassie gestured at Piper, "Well Venus, but anyway, she makes all my style choices for our big Undersea Royal Galas."

"That's a thing?" Percy sat back in his chair.

"Haha, yeah, I guess while you were off saving the world I was busy playing the family diplomat."

"She has- Persephone adores Cas," the group turned at the sound of a new voice. Nico DiAngelo stood in the doorway, his eyebrows raised in slight amusement. Behind him a dark skinned girl stood, her gold eyes glowing in the shadows.


	4. The Six

Nico and Hazel made their introductions and sat down with the others. Hazel wore a plaid dress that came down to her knees, it reminded her or the dresses the white girl's used to wear when she was growing up in New Orleans. Both her and Nico had the darkest skin of the group, but Cassie was rather tan, her skin glistened bronze as the sun set outside.

"So, I see you all have met Cassie, it's about time."

Percy sat up straighter with a frown on his face as he turned to Nico, "I've known you for years and you haven't once mentioned I have a sister."

Cassie interjected, sensing Percy' bruised feelings, "He was sworn to secrecy. On the River Styx," and collective understanding passed around the room, "we've know each other a few years, I do a lot of work in the underworld. Prospina likes it when I bring her flowers and notes from her mother."

"Prospina?"

Now it was Hazels turn to interject, "The Roman form of Persephone. They are two of the most similar counterparts I've met yet. Anyway, who are we waiting on?"

"On Thalia, Chiron mentioned the Hunters would be coming by soon so Artemis is dropping her off." Jason held Pipers hand in his lap and ruffled his hair.

"Oh yes, did you miss me baby brother?" Thalia Grace waltzed into the room her t-shirt advertising her patron goddess with a bright silver moon. The goddess herself came in behind Thalia, she looked about sixteen and had her brown hair braided messily off to the side of her face.

"Cassie!" Cassie and Thalia embraced while everyone except Thalia and Nico looked on shocked, "What? Ohhhhh, you all have only known Cassie for a few hours."

"Yeah, it's a bit strange to see a goddess and demigod being so friendly," said Annabeth

"We go way back; Cassie has provided entertainment at many a boring Gods Council. That's a Roman thing btw, but she jumps between both worlds a lot." Artemis winked.

Thalia clapped her hands, "So now that we're all here and there are no more sisterly surprises maybe we should go to bed. We passed Leo on the way in and he's working like a madman but we should be good to leave right away in the morning."


End file.
